1. Field of the Invention
The invention relates to vehicular driving assist apparatus and method for determining a locus of run to a target position and assisting the driving of a vehicle so that the vehicle follows the locus of run.
2. Description of the Related Art
A related-art technology for guiding a vehicle to a target position through the use of the automatic steering, the steering command, etc., is disclosed in, for example, Japanese Patent Application Laid-Open Publication No. 5-297935. In this related technology, errors in position, azimuth angle and curvature are measured, and a predetermined locus of run (track pattern) in which the distance of run and the curvature are associated with each other is subjected to similarity transformation so as to determine an actual control locus, as a technique for compensating for the errors.
This technology reduces the track pattern by similarity transformation, so that the vehicle can be promptly returned to the locus from a deviation therefrom if any. As an application of this technology, the track pattern may also be enlarged by similarity transformation, so that it becomes possible to set a guide path that provides a good margin for steering.
However, in the above-described technology based on similarity transformation, if the initial steering state has been set at a position other than a neutral position, the actual curvature and the curvature of a set path disagree. Therefore, since there is an initial-stage difference between the curvature of a set guide path and the actual curvature, the target direction of vehicle run cannot bring the vehicle to the target position. Furthermore, there is a case where the curvature does not become neutral even if the steering wheel is at a neutral position. Still further, if the initial steering state is limited to the neutral position, the operability of the assist operation remarkably degrades.